1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a view-angle control technique for controlling a liquid crystal drive voltage applied to each pixel.
2. Description of the Related Art
With the dramatic recent improvement in performance for liquid crystal display devices, they are used for diverse application. For example, a liquid crystal display device has been developed that allows for screen display selection between a screen based on a typical wide view angle and a screen that can be checked only by the user. Such an operation for screen selection is performed especially when the user watches a television program or creates an E-mail message with a personal digital assistant (PDA) having various functions and when advertising is displayed or the user inputs his or her password screen on an automatic teller's machine (ATM).
Such a liquid crystal display device employs a technique that aggressively utilizes the view-angle dependency of a liquid crystal display panel. Specifically, the view-angle dependency of a liquid crystal display panel is based on the fact that the front brightness, i.e., the brightness of the liquid crystal display panel when viewed from the direction of the normal line (front direction) differs from the oblique brightness, i.e., the brightness of the liquid crystal display panel when viewed from a direction having a predetermined angle with respect to the normal line (oblique direction). A liquid crystal display device employing this technique is configured to superimpose an image recognizable only when viewed from an oblique direction of a display surface of the liquid crystal display panel onto an image recognizable when viewed from the direction of the normal line to the display surface, thereby enabling only the user at the front of the device to obtain a recognizable display image.
An exemplary liquid crystal display device using this display control technique is the liquid crystal display device described in JP-A-2008-275853. The technique discussed in JP-A-2008-275853 controls the gray-scale level of each pixel to attain a gray-scale level different for each frame in order to utilize the view-angle dependency of a liquid crystal display panel based on the vertical alignment (VA) type inclusive of the multiarea vertical alignment (MVA) type. Further, the control technique is designed to selectively control the gray-scale level for each pixel such that its average brightness coincides with the brightness of image display attained when viewed from the front direction and display an image.